Dip coating has been used for coating ophthalmic lenses and optical lenses and is suitable for some coatings applied to such lenses, such as a top coat used as an anti-smudge coating to protect the underlying coating or bulk lens material from the accumulation of such dirt or grime on the lens surface and facilitate the cleaning of the lens. Such top coats have low surface energies such as 30 dynes and the highest performance top coats have very low surface energies of the order of 25 dynes.
Lenses having very low surface energies pose problems for their grinding to fit the contour of an eyeglass lens surround. For grinding, the lens must be mounted on a holding device and maintained into fixed position relative to the optical axis throughout the edge grinding operation and within narrow tolerances. When the lens has a very low surface energy, a temporary coating must be applied to the top coat, so that the contact between the lens and the holding device ensures that the required tolerances are maintained. Following the edge grinding operation, the temporary coating needs to be removed to reveal once again the underlying high performance top coat.
Conventional lower surface energy top coats are also widely used, but do not give the level of performance of very low surface energy top coats. Such conventional low surface energy top coats do not provide a high performance anti-smudge coating, but advantageously can be ground to contour without the need for a temporary coat, so that the lens can be securely held in axial alignment on the holding device.
It is also known to use dip coating for tinting ophthalmic lens.
Known dip coating apparatus for ophthalmic lenses are suitable in industrial scale coating operations. Such apparatus typically have a large high footprint, involve both relatively complicated mechanical equipment for moving lens continuously or in batches from station to station and control apparatus for controlling movement and the operating parameters of the process.
Generally speaking, there are two kinds of dip coating apparatuses. In first kind of dip coating apparatus the article, e.g., a lens, is lowered into a vat containing a coating liquid and after a predetermined coating time is removed from the vat and is allowed to dry or cure. In the second kind of dip coating apparatus, the level of the coating liquid in the vat is raised for coating and then lowered until the lens is no longer in contact with the liquid and the coated lens is dried or cured.
The manufacture of ophthalmic lenses involves many operations which may be carried out in the main production facility and other operations which are more economically or expediently carried out on the optician's premises and in particular the grinding of the lenses to fit a particular frame selected by the customer. Customers increasingly want to be able to select frames and have them fitted with prescription lenses in an hour. While it is possible for the optician to have in stock most common prescription lens blanks which can be ground to order in this reduced timeframe, the optician cannot offer the customer a choice of coatings for each such prescription lens including less expensive medium performance top coats and more expensive high performance top coats, let alone a variety of lens tints. Such customer on-site demands cannot be easily satisfied within the existing constraints of inventories, costs and timeframes.